Hannover 2003 – scientific programme

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SYBM: Biologische Moleküle in der Gasphase

SYBM 102: Biologische Moleküle in der Gasphase

SYBM 102.2: Fachvortrag

Monday, March 24, 2003, 16:30–17:00, B305

Ab initio exploration of ultrafast photochemical reaction mechanisms in aromatic biomolecules — •Wolfgang Domcke¹ and Andrzej L. Sobolewski² — ¹Institute of Physical and Theoretical Chemistry, Technical University of Munich, D-85747 Garching, Germany — ²Institute of Physics, Polish Academy of Sciences, PL-02668 Warsaw, Poland

This talk addresses the ab initio calculation of reaction paths and the corresponding energy profiles in excited electronic states of aromatic biomolecules and their clusters with water and ammonia. Indole and phenol serve as models for the investigation of the photochemistry of aromatic amino acids (tryptophan and tyrosine). Adenine is considered as an example of the DNA bases. The calculations reveal the role of hitherto uncharacterized low-lying dark excited electronic states of ¹πσ^∗ character, which intersect both the ¹ππ^∗ excited singlet states as well as the electronic ground state. The resulting conical intersections provide a pathway for ultrafast internal conversion. This mechanism can account for the photostability of these componds. In clusters of indole and phenol with water as well as ammonia, the ¹πσ^∗ states promote an intracluster hydrogen-transfer process, yielding a solvated radical pair. These findings suggest that repulsive ¹πσ^∗ states and the associated conical intersections play a universal role in the photochemistry of aromatic biomolecules (amino acids and DNA bases) in the gas phase as well as in the condensed phase.